|[February 11, 2014]
Toshiba Develops eXtremely Low Leakage SRAM (XLL SRAM) Which Enables Lower Power MCU to Fast Wake-up from a Deep Sleep Mode
TOKYO --(Business Wire)--
Corporation (TOKYO:6502) today announced that it has developed an
eXtremely Low Leakage 65nm SRAM (XLL SRAM) suitable for back-up RAM in
low power MCU that achieves a fast wake-up time from a deep sleep mode.
Toshiba presented this development at the 2014 IEEE (News - Alert) International
Solid-State Circuits Conference in San Francisco, California, on
There is strong demand for long battery discharge times in low power
systems, including wearable devices, healthcare tools and smart meter.
Although there are many challenges to reduce power of MCU used in these
systems, with advances in the process generation, increasing of leakage
current becomes problem as well as active power consumption. Reducing
leakage current in RAM (News - Alert), which retains data during stand-by, is
A typical MCU reduces power dissipation with a deep sleep mode, where
stand-by current is under 1µA. However, this makes it impossible for
typical SRAM to retain data, as SRAM require a stand-by current much
higher than 1µA. As a result, data reloading takes a long time when the
system wakes up from a deep-sleep mode. Use of FRAM as back-up RAM
eliminates this reload problem, but FRAM is much slower and consumes
more active power than SRAM and also needs more prcess cost.
Toshiba (News - Alert) has developed an eXtremely Low Leakage SRAM (XLL SRAM) that has
a leakage rate a thousand times lower than that of conventional SRAM;
27fA leakage current per bit when fabricated in 65nm process. This level
is lower than that found in published data for SRAM beyond 65nm
technology. The new SRAM can retain data for over 10 years with a single
battery charge, in a back-up memory with a capacity of around 100Kbyte.
MOSFET fabricated with recent process technology has higher gate
leakage, gate induced drain leakage (GIDL) and channel leakage. Toshiba
has developed a low leakage transistor with thick gate oxide, long
channel length and optimum source drain diffusion profile to reduce
these leakage factors, and adopt it in the SRAM memory cell. The company
has developed several innovative leakage reduction circuits. One is a
source bias circuit to apply reverse back-bias to NMOS of memory cell,
and another cuts off the supply voltage to peripheral circuits during
The low leakage transistor is larger than conventional transistor,
increasing the overall cell area. Toshiba secured a 20% reduction in
cell size compared to area designed by original design rule of this
device under the condition of 1.2V supply voltage. Generally, large
transistor circuits have higher active power dissipation. Toshiba has
suppressed this by adopting "Quarter Array Activation Scheme (QAAS)" and
"Charge Shared Hierarchical BitLine (CSHBL)" power reduction circuits.
An SRAM with a 7ns read access time is fast enough to be used as working
RAM in low power MCU and for use as back-up RAM in deep-sleep mode
because of its extremely low leakage current. As the system eliminates
data reloading, the wake-up time from deep sleep mode is boosted.
Toshiba plans to use the SRAM in a product released in 2014, and expects
to see wide use in coming battery-driven products.
Toshiba is a world-leading diversified manufacturer, solutions provider
and marketer of advanced electronic and electrical products and systems.
Toshiba Group brings innovation and imagination to a wide range of
businesses: digital products, including LCD TVs, notebook PCs, retail
solutions and MFPs; electronic devices, including semiconductors,
storage products and materials; industrial and social infrastructure
systems, including power generation systems, smart community solutions,
medical systems and escalators & elevators; and home appliances.
Toshiba was founded in 1875, and today operates a global network of more
than 590 consolidated companies, with 206,000 employees worldwide and
annual sales surpassing 5.8 trillion yen (US$61 billion). Visit
Toshiba's web site at www.toshiba.co.jp/index.htm
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